在 DefaultMQProducerImpl 的启动过程中，会校验 Topic，RocketMQ 用了了一个简易的位图来维护合法值范围，蛮小巧别致的。

public static boolean isTopicOrGroupIllegal(String str) {
    int strLen = str.length();
    int len = VALID_CHAR_BIT_MAP.length;
    boolean[] bitMap = VALID_CHAR_BIT_MAP;
    for (int i = 0; i < strLen; i++) {
        char ch = str.charAt(i);
        if (ch >= len || !bitMap[ch]) {
            return true;
        }
    }
    return false;
}


public static final boolean[] VALID_CHAR_BIT_MAP = new boolean[128];

VALID_CHAR_BIT_MAP['%'] = true;
// -
VALID_CHAR_BIT_MAP['-'] = true;
// _
VALID_CHAR_BIT_MAP['_'] = true;
// |
VALID_CHAR_BIT_MAP['|'] = true;

for (int i = 0; i < VALID_CHAR_BIT_MAP.length; i++) {
    if (i >= '0' && i <= '9') {
        // 0-9
        VALID_CHAR_BIT_MAP[i] = true;
    } else if (i >= 'A' && i <= 'Z') {
        // A-Z
        VALID_CHAR_BIT_MAP[i] = true;
    } else if (i >= 'a' && i <= 'z') {
        // a-z
        VALID_CHAR_BIT_MAP[i] = true;
    }
}